1. Field of the Invention
The present invention relates to a transmission device provided with an optical transmission line.
2. Description of the Related Art
In a transmission device constituting a network, in order to put a line in a service-in state (enable a signal to run through end-to-end), settings, such as line registration, cross-connect connection and the like must be made across the entire signal route. For this purpose, sometimes an end-to-end setting is completed beforehand and the network is made ready to be used when the termination line is connected. However, if the network is left in the state where the termination line is disconnected, optical signals cannot be received. Therefore, the transmission device regards this state as a failure, and a main signal disconnection alarm is issued. In a SDH/SONET transmission device, the alarm is transmitted along a signal route as an alarm indication signal (AIS) alarm, and is detected at all of several alarm monitor points. If the network accommodates a plurality of paths, the alarm is transmitted through the network as a path-AIS alarm, and an alarm is issued everywhere. It takes trouble equivalent to line setting to individually provide a setting for masking this path-AIS alarm at each alarm detection point. Furthermore, there is a possibility of forgetting a mask release to enable the essential alarm detection function.
In other words, if the function of a transmission device is switched on although optical signals do not run through a transmission line when a network on which transmission devices are connected through an optical transmission line is started up, the transmission device determines the state as a signal disconnection state and issues an alarm, which is a problem.
FIG. 1 explains the problem of the prior art.
FIG. 1 shows a state where a network is disconnected at the route termination part after a signal route is established between a station A and a station C through a station B. In FIG. 1, a loss-of-signal (LOS) alarm is detected at a signal input part, and an STS path alarm indication signal (AIS-P) alarm issued and transmitted after that by it is detected at each alarm detection point as an AIS-P alarm.
As prior arts there are Patent References 1 and 2.
In Patent reference 1, a test system for detecting the signal running state is built in order to remotely detect a signal running state between terminal devices. In Patent Reference 2, as a line service state, one of a non-operation state, an operation state and a temporary non-operation state can be selected. When the temporary non-operation state is selected, an alarm is prevented from terminating if the line is in an alarm state.    Patent Reference 1: Japanese Patent Application No. 2004-40441    Patent Reference 2: Japanese Patent Application No. H10-336322
Although such alarm detection is necessary as a failure occurrence notice in a service-in state, it is troublesome when the line is intentionally disconnected after the line is completed as a standby line. Although some devices have a function to mask the detection of the alarm, in that case, a masking setting must be made at each alarm detection point, and accordingly, it is troublesome.